To improve rolling resistance and running performance (wet properties) on wet road surface of a pneumatic tire, the technology of compounding silica with a rubber composition of a tread as a reinforcing agent in place of the conventional carbon black is known. With this silica compounding technology, static electricity charged in vehicles gives rise to the problems that discharge phenomenon is generated when a tire passes on manholes and the like, resulting in radio noise, adverse influence to electronic circuit parts, generation of short-circuit, and the like.
Conventionally, to solve those problems, the technology of providing a conductive member having carbon black compounded therein in a part of a tread structure, thereby securing conductivity of a tire is proposed. For example, the technology of Patent Document 1 below describes that a conductive thin film containing carbon black is arranged on the outer surfaces of a tread and a side wall, thereby discharging through this conductive layer. Furthermore, the technology of Patent Document 2 discloses that a conductive insert is provided on a tire crown part over from a tread surface to a bottom, and a conductive strip comprising a conductive material being in contact with this insert is in a contact state with a wheel in a conductive bead region, thereby discharging static electricity.
On the other hand, in recent years, many requirements for tires are demanded from the market. For example, improvement in rigidity to increase driving stability during high speed running, improvement in ride quality and in vibration absorption properties to reduce noise in vehicles, and the like, which are rubber properties in warring relationships, are required in a tread and a side wall. To satisfy those in a side wall part, a side wall rubber having a multilayer structure comprising two kinds or more of rubbers is proposed in, for example, Patent Documents 3 and 4, and is put into practical use.
Patent Document 1: JP-A-8-230407
Patent Document 2: JP-A-2006-143208
Patent Document 3: JP-A-2003-312213
Patent Document 4: JP-A-2000-25425